Glass fiber composition

ABSTRACT

The present invention provides a glass fiber composition comprising: 52 to 62 percent by weight SiO 2 , 0 to 2 percent by weight Na 2 O, 16 to 25 percent by weight CaO, 8 to 16 percent by weight Al 2 O 3 , 0.05 to 0.80 percent by weight Fe 2 O 3 , 0 to 2 percent by weight K 2 O, 1.7 to 2.6 percent by weight MgO, 0 to 10 percent by weight B 2 O 3 , 0 to 2 percent by weight TiO 2 , 0 to 2 percent by weight BaO, 0 to 2 percent by weight ZrO 2 , and 0 to 2 percent by weight SrO, and further including at least one material selected from the group consisting of: 0.05 to 1.5 percent by weight Li 2 O, 0.05 to 1.5 percent by weight ZnO, 0.05 to 3 percent by weight MnO, and 0.05 to 3 percent by weight MnO 2 , wherein the glass composition has a forming temperature of no greater than 2280° F. based on an NIST 714 reference standard and a liquidus temperature of no greater than 2155° F. In one nonlimiting embodiment of the invention, the SiO 2  content is 57 to 59 percent by weight, the Na 2 O content is up to 1 percent by weight, the CaO content is 22 to 24 percent by weight, the Al 2 O 3  content is 12 to 14 percent by weight, the Fe 2 O 3  content is up to 0.4 percent by weight, and the K 2 O content is up to 0.1 percent by weight, and the composition includes at least one material selected from the group consisting of: 0.2 to 1 percent by weight Li 2 O, 0.2 to 1 percent by weight ZnO, up to 1 percent by weight MnO, and up to 1 percent by weight MnO 2 .

CROSS REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of U.S. Provisional Application No. 60/136,538, filed May 28, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to glass compositions for making glass fibers, and more particularly to glass compositions having lowered liquidus and forming temperatures.

2. Technical Considerations

The most common glass composition for making continuous glass fiber strands for textiles and glass fiber reinforcements is “E” glass. The requirements as to what type of composition constitutes an E-glass composition are included in ASTM D578-98. An advantage of using E-glass is that its liquidus temperature is well below its forming temperature, i.e. typically greater than 100° F. (56° C.) and generally between 150° F. (83° C.) to 200° F. (111° C.). As used herein, the terms “forming temperature” and “T_(FORM)” mean the temperature of the glass at which the viscosity of the glass is log 3, or 1000 poise, and the terms “liquidus temperature” and “T_(LIQ)” mean the temperature at which solid phase (crystals) and liquid phase (melt) are in equilibrium. The difference between T_(FORM) and T_(LIQ), referred to herein as “delta T” or “ΔT”, is a common measure of the crystallization potential of a given melt composition. In the glass fiber forming industry, ΔT is typically maintained at a temperature of at least 90° F. (50° C.) in order to prevent devitrification of the molten glass in the bushing area of a glass fiber forming operation.

Boron and fluorine containing glass were developed to meet these operating conditions. More specifically, the boron and fluorine were included in the glass batch materials to act as fluxes during the glass melting operation. However, these materials are volatilized during melting and boron and fluorine emissions are released to the atmosphere. Since boron and fluorine are considered pollutants, these emissions are closely controlled by environmental regulations, which, in turn, requires careful control of the furnace operations and the use of expensive pollution control equipment. In response to this, low boron and/or low fluorine E-glasses were developed. As used herein, “low boron” means that the glass composition is no greater than 5 weight percent boron, and preferably boron-free and “low fluorine” means that the glass composition is no greater than 1 weight percent fluorine, and preferably is fluorine-free.

For example, U.S. Pat. No. 3,929,497 discloses a boron-free and fluorine-free glass composition containing titanium dioxide in the range of 0.5 to 5 percent by weight and Fe₂O₃ in the range of 5 to 15 percent by weight.

U.S. Pat. No. 4,199,364 discloses a boron-free and fluorine-free glass composition that contains Li₂O in the range of 0.1 to 1.5 percent by weight and may also include barium oxide. The liquidus temperature of the compositions is over 2200° F.

U.S. Pat. No. 4,542,106 discloses a boron-free and fluorine-free glass composition that contains 1 to 5 percent by weight TiO₂. The fibers also have a seed count of 5 seeds or less per cubic centimeter of glass and an electrical leakage value of 2.8 nanoamperes or less.

U.S. Pat. No. 5,789,329 discloses a boron-free and fluorine-free glass composition that contains up to 0.9 percent by weight TiO₂ and has a ΔT of at least 100° F. (56° C.).

For additional information concerning glass compositions and methods for fiberizing the glass composition, see K. Loewenstein, The Manufacturing Technology of Continuous Glass Fibres, (3d Ed. 1993) at pages 30-44, 47-60, 115-122 and 126-135, and F. T. Wallenberger (editor), Advanced Inorganic Fibers: Processes, Structures, Properties, Applications, (2000) at pages 81-102 and 129-168, which are hereby incorporated by reference.

Because the actual fiber forming operation is conducted at high temperatures, there are high energy costs associated with its production. In addition, the high temperatures accelerate the degradation of the refractory used in the glass melting furnace as well as the bushings used to form the fibers. The bushings include precious metals that cannot be recovered from the glass as the bushings corrode. It would be advantageous to produce the glass fibers at the lowest possible forming and liquidus temperatures so as to reduce the energy costs and thermal load on the furnace refractory and bushings, while at the same time provide the ΔT required to ensure an uninterrupted glass fiber forming operation. Reducing the forming and liquidus temperatures of the glass compositions can also result in environmental benefits, such as but not limited to, a reduction in the amount of fuel required to generate the energy necessary for the fiber forming operation, as well as a reduction in the flue gas temperature. In addition, it would be advantageous if the glass compositions are low fluoride and/or low boron compositions, and preferably are fluorine-free and/or boron-free, so as to reduce or eliminate the environmental pollutants associated with these materials.

SUMMARY OF THE INVENTION

The present innovation provides a glass fiber composition comprising: 52 to 62 percent by weight SiO₂, 0 to 2 percent by weight Na₂O, 16 to 25 percent by weight CaO, 8 to 16 percent by weight Al₂O₃, 0.05 to 0.80 percent by weight Fe₂O₃, 0 to 2 percent by weight K₂O, 1.7 to 2.9 percent by weight MgO, 0 to 10 percent by weight B₂O₃, 0 to 2 percent by weight TiO₂, 0 to 2 percent by weight BaO, 0 to 2 percent by weight ZrO₂, and 0 to 2 percent by weight SrO, wherein the glass composition has a forming temperature of no greater than 2280° F. based on an NIST 714 reference standard and a liquidus temperature of no greater than 2155° F. In one nonlimiting embodiment of the invention, the glass fiber composition further includes at least one material selected from the group consisting of: 0.05 to 1.5 percent by weight Li₂O, 0.05 to 1.5 percent by weight ZnO, 0.05 to 3 percent by weight MnO, and 0.05 to 3 percent by weight MnO₂.

The present invention also provides a glass fiber composition consisting essentially of: 52 to 62 percent by weight SiO₂, 0 to 2 percent by weight Na₂O, 16 to 25 percent by weight CaO, 8 to 16 percent by weight Al₂O₃, 0.05 to 0.80 percent by weight Fe₂O₃, 0 to 2 percent by weight K₂O, 2.2 to 2.9 percent by weight MgO, 0 to 10 percent by weight B₂O₃, 0 to 2 percent by weight TiO₂, 0 to 2 percent by weight BaO, 0 to 2 percent by weight ZrO₂, and 0 to 2 percent by weight SrO, wherein the glass composition has a forming temperature of no greater than 2280° F. based on an NIST 714 reference standard and a liquidus temperature of no greater than 2155° F.

The present innovation provides a glass fiber composition comprising: 52 to 62 percent by weight SiO₂, 0 to 2 percent by weight Na₂O, 16 to 25 percent by weight CaO, 8 to 16 percent by weight Al₂O₃, 0.05 to 0.80 percent by weight Fe₂O₃, 0 to 2 percent by weight K₂O, 1.7 to 2.6 percent by weight MgO, 0 to 10 percent by weight B₂O₃, 0 to 2 percent by weight TiO₂, 0 to 2 percent by weight BaO, 0 to 2 percent by weight ZrO₂, and 0 to 2 percent by weight SrO, and further including at least one material selected from the group consisting of: 0.05 to 1.5 percent by weight Li₂O, 0.05 to 1.5 percent by weight ZnO, 0.05 to 3 percent by weight MnO, and 0.05 to 3 percent by weight MnO₂, wherein the glass composition has a forming temperature of no greater than 2280° F. based on an NIST 714 reference standard and a liquidus temperature of no greater than 2155° F. In one nonlimiting embodiment of the invention, the SiO₂ content is 57 to 59 percent by weight, the Na₂O content is up to 1 percent by weight, the CaO content is 22 to 24 percent by weight, the Al₂O₃ content is 12 to 14 percent by weight, the Fe₂O₃ content is up to 0.4 percent by weight, and the K₂O content is up to 0.1 percent by weight, and the composition includes at least one material selected from the group consisting of: 0.2 to 1 percent by weight Li₂O, 0.2 to 1 percent by weight ZnO, up to 1 percent by weight MnO, and up to 1 percent by weight MnO₂.

BRIEF DESCRIPTION OF THE FIGURE

FIGS. 1 and 2 are graphs showing the relation between the amount of MgO and the liquidus temperature for glass fiber compositions of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The base composition for the glass fibers of the present invention suitable for textiles and glass fiber reinforcements includes the following main constituents in weight percent (wt %) based on the total weight of the final glass composition.

broad range preferred range most preferred range SiO₂ (wt %) 52 to 62 55 to 61 57 to 59 Na₂O (wt %) 0 to 2 up to 1.5 up to 1   CaO (wt %) 16 to 25 20 to 25 22 to 24 Al₂O₃ (wt %)  8 to 16 11 to 14 12 to 14 Fe₂O₃ (wt %) 0.05 to 0.80 up to 0.5 up to 0.4 K₂O (wt %) 0 to 2 up to 1   up to 0.1

It should be appreciated that numerical values discussed herein, such as but not limited to weight percent of materials, length of time or temperatures, are approximate and are subject to variations due to various factors well known to those skilled in the art such as, but not limited to, measurement standards, equipment and techniques. For example, where it states in the present application that the range for SiO₂ is 52 to 62 weight percent, this range is about 52 to about 62 weight percent, and where it states that the forming temperature of a glass composition should be no greater than 2280° F. (1249° C.), the temperature is about 2280° F.

MgO is also a main constituent of the glass compositions of the present invention. It has been found that the heating and melting profile of a glass fiber composition, and in particular the liquidus temperature, can be controlled and in particular optimized by controlling the amount of MgO, which an object of the present invention and will be discussed later in more detail.

Oftentimes additional materials are added to the glass composition to modify the melt properties of the glass. For example, and without limiting the present invention, Li₂O, ZnO₂, MnO and MnO₂ can be added to the glass fiber composition to reduce T_(LIQ). In one nonlimiting embodiment of the glass fibers of the present invention, the glass composition can include one or more of these materials in the following amounts.

broad range preferred range Li₂O (wt %) 0.05 to 1.5 0.2 to 1 ZnO (wt %) 0.05 to 1.5 0.2 to 1 MnO (wt %) 0.05 to 3 up to 1 MnO₂ (wt %) 0.05 to 3 up to 1

It is believed that levels of these materials less than 0.05 wt % would be considered either tramp amounts or so low that they will not materially impact the glass melt properties.

Boron is another material that can be added to glass fiber compositions to reduce T_(LIQ). However, as discussed earlier, the inclusion of boron results in the production of particulates that, depending on the particulate level, may have to be removed from a melting furnace exhaust stream before being released into the environment. Although the amount of B₂O₃ in a glass fiber composition can be as high as 10 wt %, one nonlimiting embodiment of a glass composition of the present invention includes no greater than 3 wt % B₂O₃, preferably no greater than 2 wt % B₂O₃, and more preferably no greater than 1 wt % B₂O₃. In another nonlimiting embodiment of the invention, the glass composition is essentially boron-free, i.e. it includes no more than a trace amount of B₂O₃, which is considered herein to be up to 0.05 wt % B₂O₃, and preferably does not include any B₂O₃.

It should be appreciated that glass fiber compositions can include other constituents and the present invention contemplates the inclusion of other materials in the glass fiber compositions, such as but not limited to, 0 to 2 wt % each of TiO₂, BaO, ZrO₂ and SrO.

In addition, because of the environmental concerns discussed earlier, although not limiting in the present invention, the glass compositions are preferably low fluorine compositions, i.e. no greater than 0.30 wt % fluorine, and more preferably are fluorine-free, i.e. it includes no more than a trace amount of fluorine, which is considered herein to be up to 0.05 wt % fluorine, and preferably does not include any fluorine.

It should be appreciated that the glass compositions disclosed herein can also include small amounts of other materials, for example melting and refining aids, tramp materials or impurities. For example and without limiting the present invention, melting and fining aids, such as SO₃, are useful during production of the glass, but their residual amounts in the glass can vary and have no material effect on the properties of the glass product. In addition, small amounts of the additives discussed above can enter the glass composition as tramp materials or impurities included in the raw materials of the main constituents.

Commercial glass fibers of the present invention can be prepared in the conventional manner well known in the art, by blending the raw materials used to supply the specific oxides that form the composition of the fibers. For example, typically sand is used for SiO₂, clay for Al₂O₃, lime or limestone for CaO, and dolomite for MgO and some of the CaO. As discussed earlier, the glass can include other additives that are added to modify the glass properties as well as small amounts of melting and refining aids, tramp materials or impurities.

After the ingredients are mixed in the proper proportions to provide the desired weight of each constituent for the desired glass, the batch is melted in a conventional glass fiber melting furnace and the resulting molten glass is passed along a conventional forehearth and into a glass fiber forming bushing located along the bottom of the forehearth, as is well known to those skilled in the art. During the glass melting phase, the glass is typically heated to a temperature of at least 2550° F. (1400° C.). The molten glass is then drawn or pulled through a plurality of holes in the bottom of the bushing. The streams of molten glass are attenuated to filaments by winding a strand of filaments on a forming tube mounted on a rotatable collet of a winding machine. Alternatively, the fiber forming apparatus can be, for example, a forming device for synthetic textile fibers or strands in which fibers are drawn from nozzles, such as but not limited to a spinneret, as is known to those skilled in the art. Typical forehearths and glass fiber forming arrangements are shown in K. Loewenstein, The Manufacturing Technology of Continuous Glass Fibres, (Third Edition 1993) at pages 85-107 and pages 115-135, which are hereby incorporated by reference.

Tables 1-7 show laboratory examples of glass fiber compositions that illustrate the effect of MgO on the liquidus temperature of the glass compositions. Boron and fluorine were not included in these compositions.

The glass fiber compositions shown in Tables 1-7 were prepared from reagent grade oxides (e.g., pure silica or calcia). The batch size for each example was 1000 grams. The individual batch ingredients were weighed out, combined and placed in a tightly sealed jar. The sealed jar was then placed in a paint shaker for 15 minutes to effectively mix the ingredients. A portion of the batch was then place into a platinum crucible, filling no more than ¾ of its volume. The crucible was then placed in a furnace and heated to 2600° F. (1425° C.) for 15 minutes. The remaining batch was then added to the hot crucible and heated to 2600° F. (1425° C.) for 15 to 30 minutes. The furnace temperature was then raised to 2700° F. (1482° C.) and held there for 4 hours. The molten glass was then fritted in water and dried. The forming temperature, i.e. the glass temperature at a viscosity of 1000 poise, was determined by ASTM method C965-81, and the liquidus temperature by ASTM method C829-81.

The weight percent of the constituents of the compositions shown in Tables 1-7 are based on the weight percent of each constituent in the batch. It is believed that the batch weight percent is generally about the same as the weight percent of the melted sample, except for glass batch materials that volatilize during melting, e.g. boron and fluorine. For boron, it is believed that the weight percent of B₂O₃ in a laboratory samples will be 5 to 10 percent less than the weight percent of B₂O₃ in the batch composition. For fluorine, it is believed that the weight percent of fluorine in a lab melt will be about 50 percent less than the weight percent of fluorine in the batch composition. It is further believed that glass fiber compositions made from commercial grade materials and melted under conventional operating conditions will have similar batch and melt weight percents as discussed above, except that the batch and melt weight percents for the volatile components of the composition will actually be closer to each other than the batch and melt wt % of the laboratory melts because in a conventional melting operation, the materials are exposed to the high melting temperatures for less time than the 4 hours of exposure for the laboratory melts.

Determination of the high temperature viscosity, T_(FORM), was based on the glass samples being compared against physical standards supplied by the National Institute of Standards and Testing (NIST). In Tables 1-7, T_(FORM) is reported based on comparison to either NIST 717A, which is a borosilicate glass standard, or NIST 714, which is a soda lime glass standard. Although either standard can be used, it is believed that the NIST 714 reference standard is more reliable because it has been observed that the NIST borosilicate standard 717A deteriorates at temperatures greater than 2150° F. (1177° C.). In comparing T_(FORM) based on the two different standards, generally T_(FORM) based on NIST 714 is 20° F. to 25° F. (11° C. to 16° C.) higher than T_(FORM) based on NIST 717A. The T_(LIQ) is unaffected by the NIST standard.

Examples 1-7 in Table 1 show the change in the liquidus temperature of a typical glass fiber forming composition that further includes 1 wt % TiO₂, as the amount of MgO is varied from 1.82 to 3 wt %. Examples 8-14 in Table 2 and Examples 15-30 in Table 3 show the change in the liquidus temperature of a typical glass fiber forming composition that further includes 1.5 or 1.1 wt % TiO₂, respectively, and 0.90 wt % Li₂O, as the amount of MgO is varied from 1.7 to 3.5 wt %. Examples 31-38 in Table 4 show the change in the liquidus temperature of a typical glass fiber forming composition that further includes 0.5 wt % TiO₂ and 0.90 wt % Li₂O, as the amount of MgO is varied from 1.7 to 3.12 wt %. Examples 39-49 in Table 5 show the change in the liquidus temperature of a typical glass fiber forming composition that further includes 1.1 wt % TiO₂, 0.45 wt % Li₂O and 0.45 wt % ZnO, as the amount of MgO is varied from 1.7 to 3.1 wt %. Examples 47-54 in Table 6 show the change in the liquidus temperature of a typical glass fiber forming composition that further includes 1.1 wt % TiO₂ and 0.90 wt % ZnO, as the amount of MgO is varied from 1.7 to 3.1 wt %. Examples 59-66 in Table 7 show the change in the liquidus temperature of a typical glass fiber forming composition that further includes 1.1 wt % TiO₂, 0.30 wt % Na₂O, 0.60 wt % Li₂O and 0.25 wt % Fe₂O₃ as the amount of MgO is varied from 1.7 to 3.1 wt %. In addition, the forming temperatures for selected glass compositions are also included in Tables 1-7.

Tables 1-7 also include the ratio SiO₂/RO, which is the ratio of the silica content of the batch, expressed as SiO₂, to the sum of the calcia and magnesia content, expressed as CaO and MgO, respectively.

TABLE 1 Ex. 1 Ex. 2* Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 SiO₂ (wt %) 59.83 59.61 60.13 60.43 60.43 59.61 59.61 Al₂O₃ (wt %) 12.21 12.16 12.27 12.39 12.33 12.16 12.16 CaO (wt %) 22.80 23.51 22.92 23.14 23.03 24.31 24.31 MgO (wt %) 3.00 2.62 2.50 2.00 2.00 1.82 1.82 TiO₂ (wt %) 1.00 1.00 1.00 1.00 1.00 1.00 1.00 Na₂O (wt %) 0.96 0.90 0.98 1.01 1.01 0.90 0.90 Fe₂O₃ (wt %) 0.20 0.20 0.20 0.20 0.20 0.20 0.20 SiO₂/RO 2.32 2.28 2.37 2.40 2.41 2.28 2.28 T_(FORM) (° F.) 2265 2309 2278 @ NIST 714 T_(LIQ) (° F.) 2160 2138 2127 2149 2154 2161 2182 ΔT (° F.) 127 182 94 *average of five samples

TABLE 2 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 SiO₂ (wt %) 59.62 59.30 59.97 60.09 60.21 60.33 60.75 Al₂O₃ (wt %) 12.12 12.10 12.19 12.22 12.24 12.24 12.35 CaO (wt %) 22.12 22.60 22.25 22.30 22.34 22.39 22.55 MgO (wt %) 3.50 3.40 2.90 2.70 2.50 2.30 1.70 TiO₂ (wt %) 1.50 1.50 1.50 1.50 1.50 1.50 1.50 Li₂O (wt %) 0.90 0.90 0.90 0.90 0.90 0.90 0.90 Fe₂O₃ (wt %) 0.25 0.20 0.25 0.25 0.25 0.25 0.25 SiO₂/RO 2.33 2.28 2.38 2.40 2.42 2.44 2.51 NIST 717A T_(FORM) (° F.) 2196 2197 2192 2196 2223 2239 T_(LIQ) (° F.) 2158 2136 2122 2152 2124 2120 2131 ΔT (° F.) 38 75 40 72 103 108 NIST 714 T_(FORM) (° F.) 2219 2223 2215 2219 2248 2264 T_(LIQ) (° F.) 2158 2136 2122 2152 2124 2120 2131 ΔT (° F.) 61 101 63 95 128 133

TABLE 3 Ex. 15 Ex. 16 Ex. 17 Ex. 18 Ex. 19 Ex. 20 Ex. 21 Ex. 23 SiO₂ (wt %) 59.61 59.61 59.73 59.85 59.97 60.09 60.10 60.10 Al₂O₃ (wt %) 12.92 12.92 12.92 12.95 12.97 13.00 13.00 13.00 CaO (wt %) 21.91 21.96 22.00 22.04 22.09 22.13 22.15 22.15 MgO (wt %) 3.50 3.30 3.10 2.90 2.70 2.50 2.50 2.50 TiO₂ (wt %) 1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.10 Li₂O (wt %) 0.90 0.90 0.90 0.90 0.90 0.90 0.9 0.9 Fe₂O₃ (wt %) 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 SiO₂/RO 2.35 2.36 2.38 2.40 2.42 2.44 2.44 2.44 NIST 717A T_(FORM) (° F.) T_(LIQ) (° F.) 2154 2138 2127 2122 2120 2111 ΔT (° F.) NIST 714 T_(FORM) (° F.) 2215 2215 2217 2217 2226 2233 2255 2259 T_(LIQ) (° F.) 2154 2138 2127 2122 2120 2111 2070 2077 ΔT (° F.) 61 77 90 95 106 122 185 182 Ex. 23 Ex. 24 Ex. 25 Ex. 26 Ex. 27 Ex. 28 Ex. 29 Ex. 30 SiO₂ (wt %) 60.21 60.00 60.33 59.95 60.00 59.90 60.57 59.85 Al₂O₃ (wt %) 13.02 12.40 13.05 12.40 12.50 12.40 13.10 12.0 CaO (wt %) 22.18 22.05 22.22 23.30 23.70 23.55 22.31 23.80 MgO (wt %) 2.30 2.30 2.10 2.10 1.90 1.90 1.70 1.70 TiO₂ (wt %) 1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.10 Li₂O (wt %) 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 Fe₂O₃ (wt %) 0.25 0.25 0.25 0.25 0.25 0.25 0.26 0.25 SiO₂/RO 2.46 2.46 2.48 2.36 2.34 2.35 2.52 2.35 NIST 717A T_(FORM) (° F.) 2226 2221 2273 2223 2237 2235 2210 T_(LIQ) (° F.) 2088 2095 2077 2106 2082 2120 2086 2113 ΔT (° F.) 138 126 196 117 155 149 97 NIST 714 T_(FORM) (° F.) 2251 2246 2296 2248 2262 2235 2262 2235 T_(LIQ) (° F.) 2088 2095 2077 2106 2082 2113 2086 2113 ΔT (° F.) 163 151 219 142 180 122 176 122

TABLE 4 Ex. 31 Ex. 32 Ex. 33 Ex. 34 Ex. 35 Ex. 36 Ex. 37 Ex. 38 SiO₂ (wt %) 60.05 59.97 60.09 60.21 60.23 60.23 60.33 60.76 Al₂O₃ (wt %) 12.98 12.19 12.22 12.24 12.25 12.25 12.27 12.35 CaO (wt %) 22.14 23.56 23.31 23.35 23.36 23.36 23.40 23.56 MgO (wt %) 3.12 2.90 2.70 2.50 2.50 2.50 2.30 1.70 TiO₂ (wt %) 0.55 0.50 0.50 0.50 0.51 0.51 0.50 0.50 Li₂O (wt %) 0.91 0.90 0.90 0.90 0.9 0.9 0.90 0.90 Fe₂O₃ (wt %) 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 SiO₂/RO 2.38 2.27 2.31 2.33 2.33 2.33 2.35 2.41 NIST 717A T_(FORM) (° F.) 2264 2181 2197 2192 2196 2201 T_(LIQ) (° F.) 2136 2138 2125 2124 2120 2116 2131 2149 ΔT (° F.) 128 43 72 68 65 52 NIST 714 T_(FORM) (° F.) 2205 2223 2215 2228 2235 2221 2226 T_(LIQ) (° F.) 2136 2138 2125 2124 2120 2116 2131 2149 ΔT (° F.) 68 98 91 108 119 90 77

TABLE 5 Ex. 39 Ex. 40 Ex. 41 Ex. 42 Ex. 43 Ex. 44 Ex. 45 Ex. 46 Ex. 47 Ex. 48 Ex. 49 SiO₂ (wt %) 59.73 59.85 59.97 60.09 60.21 60.33 59.54 60.45 59.47 60.57 59.40 Al₂O₃ (wt %) 12.92 12.95 12.97 13.00 13.02 13.05 12.16 13.08 12.16 13.10 12.16 CaO (wt %) 22.00 22.04 22.09 22.13 22.18 22.22 23.95 22.27 24.22 22.31 24.49 MgO (wt %) 3.10 2.90 2.70 2.50 2.30 2.10 2.10 1.90 1.90 1.70 1.70 TiO₂ (wt %) 1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.10 Li₂O (wt %) 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 ZnO (wt %) 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 Fe₂O₃ (wt %) 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 SiO₂/RO 2.38 2.40 2.42 2.44 2.46 2.48 2.29 2.50 2.28 2.52 2.27 NIST 717A T_(FORM) (° F.) 2242 2248 2250 2259 2257 2273 2241 2273 2278 2248 T_(LIQ) (° F.) 2142 2134 2109 2097 2091 2084 2111 2082 2118 2075 2134 ΔT (° F.) 100 114 141 162 166 189 130 191 203 114 NIST 714 T_(FORM) (° F.) 2268 2275 2275 2284 2284 2300 2266 2300 2224 2305 2273 T_(LIQ) (° F.) 2142 2134 2109 2097 2091 2084 2111 2082 2118 2075 2134 ΔT (° F.) 124 141 166 187 193 216 155 218 106 230 139

TABLE 6 Ex. 50 Ex. 51 Ex. 52 Ex. 53 Ex. 54 Ex. 55 Ex. 56 Ex. 57 Ex. 58 SiO₂ (wt %) 59.73 59.85 59.97 58.80 60.09 60.21 60.33 60.45 60.57 Al₂O₃ (wt %) 12.92 12.95 12.97 13.33 13.00 13.02 13.05 13.08 13.10 CaO (wt %) 22.00 22.04 22.09 23.45 22.13 22.18 22.22 22.27 22.31 MgO (wt %) 3.10 2.90 2.70 2.50 2.50 2.30 2.10 1.90 1.70 TiO₂ (wt %) 1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.10 ZnO (wt %) 0.90 0.90 0.90 0.9 0.90 0.90 0.90 0.90 0.90 Fe₂O₃ (wt %) 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 SiO₂/RO 2.38 2.40 2.42 2.27 2.44 2.46 2.48 2.50 2.52 NIST 717A T_(FORM) (° F.) 2282 2286 2296 2287 2304 2296 2307 2316 2298 T_(LIQ) (° F.) 2138 2131 2118 2129 2115 2131 2136 2128 2140 ΔT (° F.) 144 155 178 158 189 165 171 178 158 NIST 714 T_(FORM) (° F.) 2309 2313 2323 2314 2332 2323 2336 2345 2327 T_(LIQ) (° F.) 2138 2131 2118 2129 2115 2131 2136 2138 2140 ΔT (° F.) 171 182 205 185 217 192 200 207 187

TABLE 7 Ex. 59 Ex. 60 Ex. 61 Ex. 62 Ex. 63 Ex. 64 Ex. 65 Ex. 66 SiO₂ (wt %) 59.80 59.75 59.70 59.65 59.60 59.55 59.50 59.45 Al₂O₃ (wt %) 12.25 12.25 12.25 12.25 12.25 12.25 12.25 12.25 CaO (wt %) 22.69 22.85 22.85 23.35 23.60 23.85 24.10 24.35 MgO (wt %) 3.10 2.90 2.70 2.50 2.30 2.10 1.90 1.70 TiO₂ (wt %) 1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.10 Na₂O (wt %) 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 Li₂O (wt %) 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 Fe₂O₃ (wt %) 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 SiO₂/RO 2.33 2.32 2.34 2.31 2.30 2.29 2.29 2.28 NIST 717A T_(FORM) (° F.) 2239 2242 2232 2235 2228 2228 2228 T_(LIQ) (° F.) 2113 2113 2111 2118 2133 2143 2158 2178 ΔT (° F.) 126 131 113 103 85 70 50 NIST 714 T_(FORM) (° F.) 2264 2257 2268 2257 2260 2253 2253 2253 T_(LIQ) (° F.) 2113 2113 2111 2118 2133 2143 2158 2178 ΔT (° F.) 151 144 157 139 127 110 95 75

FIGS. 1 and 2 present curves illustrating the relationship between the forming temperature of the compositions shown in Tables 1-7 versus the amount of MgO, as discussed below in more detail. These curves are 2nd order polynomial curves generated using Microsoft® Excel 97 SR-2(f). Each of the curves shows that the amount of MgO impacts the liquidus temperature and in particular, there is a eutectic, i.e. minimum, in the liquidus temperature vs. the amount of MgO, indicating that the amount of MgO can be controlled to generate a minimum liquidus temperature for a glass fiber forming composition.

More specifically, Curve 1 in FIG. 1 illustrates the relationship between the liquidus temperature and the amount of MgO in the glass compositions shown in Examples 1-7 in Table 1. In order to expand the MgO range to 3.5 weight percent, a control composition was also included in the curve. The control composition included 59.37 wt % SiO₂, 12.94 wt % Al₂O₃, 21.00 wt % CaO, 3.5 wt % MgO, 1.42 wt % TiO₂, 1.01 wt % NaO and 0.22 wt % Fe₂O₃, and had a T_(LiQ) of 2158° F. As can be seen, based on this curve, the liquidus temperature approaches a minimum in the range of 2.2 to 2.9 wt % MgO, and reaches a minimum temperature at 2.45 to 2.65 wt % MgO.

Curve 2 in FIG. 1 illustrates the relationship between the liquidus temperature and the amount of MgO in the glass compositions shown in Examples 8-14 in Table 2. As can be seen, based on this curve, the liquidus temperature approaches a minimum in the range of 1.85 to 2.6 wt % MgO, and reaches a minimum temperature at 2.0 to 2.45 wt % MgO.

Curve 3 in FIG. 1 illustrates the relationship between the liquidus temperature and the amount of MgO in the glass compositions shown in Examples 15-30 in Table 3. As can be seen, based on this curve, the liquidus temperature approaches a minimum in the range of 1.8 to 2.5 wt % MgO, and reaches a minimum temperature at 2.0 to 2.3 wt % MgO.

Curve 4 in FIG. 1 illustrates the relationship between the liquidus temperature and the amount of MgO in the glass compositions shown in Examples 31-38 in Table 4. As can be seen, based on this curve, the liquidus temperature approaches a minimum in the range of 2.3 to 2.7 wt % MgO, and reaches a minimum temperature at 2.35 to 2.6 wt % MgO.

Curve 5 in FIG. 1 illustrates the relationship between the liquidus temperature and the amount of MgO in the glass compositions shown in Examples 39-49 in Table 5. As can be seen, based on this curve, the liquidus temperature approaches a minimum in the range of 1.8 to 2.5 wt % MgO, and reaches a minimum temperature at 2.0 to 2.3 wt % MgO.

Curve 6 in FIG. 1 illustrates the relationship between the liquidus temperature and the amount of MgO in the glass compositions shown in Examples 50-58 in Table 6. As can be seen, based on this curve, the liquidus temperature approaches a minimum in the range of 2.3 to 2.7 wt % MgO, and reaches a minimum temperature at 2.4 to 2.6 wt % MgO.

Curve 7 in FIG. 1 illustrates the relationship between the liquidus temperature and the amount of MgO in the glass compositions shown in Examples 59-66 in Table 7. The control sample discussed above was incorporated into Curve 7. As can be seen, based on this curve, the liquidus temperature approaches a minimum in the range of 2.7 to 3.2 wt % MgO, and reaches a minimum temperature at 2.8 to 3.1 wt % MgO.

As can be seen in Curves 1-7, the amount of MgO impacts the liquidus temperature and in particular, the amount of MgO can be controlled to generate a minimum liquidus temperature for a glass fiber forming composition.

FIG. 2 Illustrates the relationship between the liquidus temperature and the amount of MgO for various combinations of Examples 8-58 in Tables 2-6. More specifically, Curve A plots the liquidus temperature versus the amount of MgO for the glass compositions shown in Tables 2, 3, and 4, Curve B plots the liquidus temperature versus the amount of MgO for the glass compositions shown in Tables 3, 5 and 6, and Curve C plots the liquidus temperature versus the amount of MgO for the glass compositions shown in Tables 2-6. It is appreciated that Curves A, B and C combine the liquidus temperature for different glass compositions. More specifically, the glass compositions represented by Curve A have the same Li₂O level but differ in the amount of TiO₂, the glass compositions represented by Curve B have the same amount of TiO₂ but differ in the amount of Li₂O and ZnO (although the total amount of Li₂O+ZnO is the same), and the glass compositions represented by Curve C differ in the amounts of TiO₂, Li₂O and/or ZnO. However, these combinations are offered to illustrate the trend in the liquidus temperature as the amount of MgO varies.

Referring to FIG. 2, it can be seen that the liquidus temperature for Curves A, B and C approaches a minimum in the range of 1.7 to 2.65 wt % MgO, and reaches a minimum temperature at 1.90 to 2.55 wt % MgO.

The fact that the glass compositions of Tables 2-6 exhibit a minimum liquidus temperature (as shown in Curves 2-6, A, B and C) than the glass compositions of Table 1 (as shown in Curve 1) is to be expected since Examples 8-58 in Tables 2-6 all included additives, and in particular, Li₂O and/or ZnO, which reduce liquidus temperature. However, of particular significance is the fact that the minimum liquidus temperatures for the glass compositions of Tables 2-6 are generally within an MgO range lower than that of the glass compositions of Table 1.

In viewing Curves 1-7 and A-C in FIGS. 1 and 2, it is clear that the amount of MgO impacts the heating and melting profile of a glass fiber forming compositions, and in particular, the MgO content can be used to minimize the liquidus temperature of a glass fiber forming composition and allow for a lower forming temperature while maintaining the ΔT required to facilitate a continuous and uninterrupted glass fiber forming operation.

Examples 67-98 in Table 8 are additional examples of glass compositions of the present invention having 2.3 to 2.55 wt % MgO and a AT of greater than 90° F. based on a NIST 714 reference standard. These laboratory samples include up to 3 wt % B₂O₃, up to 0.9 wt % Na₂O, up to 1.1 wt % TiO₂, up to 0.9 wt % Li₂O, p to 1 wt % ZnO, up to 3 wt % MnO, and up to 3 wt % MnO₂ based on their batch composition, as discussed earlier. The samples were made in the same manner as those in Tables 1-7.

TABLE 8 Ex. 67 Ex. 68** Ex. 69 Ex. 70 Ex. 71 Ex. 72 Ex. 73 Ex. 74 SiO₂ (wt %) 60.12 59.61 59.11 58.61 60.12 59.01 59.31 59.61 Al₂O₃ (wt %) 13.00 12.16 12.16 12.16 13.00 12.04 12.10 12.16 CaO (wt %) 21.13 23.50 23.00 23.50 21.13 23.27 23.38 23.50 MgO (wt %) 2.50 2.50 2.50 2.50 2.50 2.48 2.49 2.50 TiO₂ (wt %) 1.10 1.10 1.10 1.10 1.10 1.09 1.09 1.10 B₂O₃ (wt %) 1.00 0.30 1.00 1.00 1.00 1.00 0.50 0.50 Na₂O (wt %) 0.89 0.89 Li₂O (wt %) 0.20 0.90 0.90 0.90 0.50 ZnO (wt %) 0.90 0.20 MnO (wt %) 0.20 MnO₂ (wt %) Fe₂O₃ (wt %) 0.25 0.23 0.23 0.23 0.25 0.23 0.23 0.23 SiO₂/RO 2.54 2.29 2.32 2.25 2.54 2.29 2.29 2.29 NIST 717A T_(FORM) (° F.) 2235 2247 2178 2172 2318 2260 2255 2221 T_(LIQ) (° F.) 2082 2099 2088 2088 2172 2152 2154 2111 ΔT (° F.) 153 148 90 79 146 108 101 110 NIST 714 T_(FORM) (° F.) 2260 2272 2201 2194 2345 2286 2280 2246 T_(LIQ) (° F.) 2082 2099 2088 2088 2172 2152 2154 2111 ΔT (° F.) 178 173 113 106 173 134 126 135 Ex. 75 Ex. 76 Ex. 77 Ex. 78 Ex. 79** Ex. 80** Ex. 81** Ex. 82 SiO₂ (wt %) 59.40 59.20 59.61 59.61 59.61 57.72 59.61 58.61 Al₂O₃ (wt %) 12.16 12.16 12.16 12.16 12.16 11.80 12.16 12.16 CaO (wt %) 23.49 23.69 23.50 23.50 20.50 22.80 20.50 23.50 MgO (wt %) 2.30 2.30 2.50 2.50 2.50 2.52 2.50 2.50 TiO₂ (wt %) 1.10 1.10 1.10 1.10 1.10 1.07 1.10 1.10 B₂O₃ (wt %) 0.30 0.45 1.00 Na₂O (wt %) 0.40 0.40 0.90 0.87 0.90 Li₂O (wt %) 0.45 0.45 0.30 0.30 ZnO (wt %) 0.45 0.45 0.30 0.45 0.30 MnO (wt %) 3.00 0.30 MnO₂ (wt %) 3.00 3.00 Fe₂O₃ (wt %) 0.25 0.25 0.23 0.23 0.23 0.22 0.23 0.23 SiO₂/RO 2.30 2.28 2.29 2.29 2.59 2.28 2.59 2.25 NIST 717A T_(FORM) (° F.) 2246 2250 2235 2271 2221 2196 2224 2226 T_(LIQ) (° F.) 2118 2105 2113 2113 2117 2125 2118 2082 ΔT (° F.) 128 145 122 158 104 71 106 144 NIST 714 T_(FORM) (° F.) 2273 2277 2260 2298 2245 2219 2249 2251 T_(LIQ) (° F.) 2118 2105 2113 2113 2117 2125 2118 2082 ΔT (° F.) 155 172 147 185 128 94 131 169 Ex. 83 Ex. 84 Ex. 85 Ex. 86 Ex. 87 Ex. 88 Ex. 89 Ex. 90 SiO₂ (wt %) 58.96 58.70 58.35 57.65 58.15 57.95 58.20 58.10 Al₂O₃ (wt %) 13.24 13.35 13.20 13.40 13.20 13.20 13.03 13.03 CaO (wt %) 23.65 23.50 23.65 24.15 22.85 24.05 23.64 23.74 MgO (wt %) 2.5 2.50 2.55 2.55 2.55 2.55 2.50 2.50 TiO₂ (wt %) .50 0.50 1.10 1.10 1.10 1.10 0.50 0.50 B₂O₃ (wt %) Na₂O (wt %) 0.30 Li₂O (wt %) 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90 ZnO (wt %) 1.00 1.00 1.00 1.00 MnO (wt %) MnO₂ (wt %) Fe₂O₃ (wt %) 0.25 0.25 0.25 0.25 0.25 0.25 0.23 0.23 SiO₂/RO 2.25 2.26 2.23 2.16 2.29 2.18 2.23 2.21 NIST 717A T_(FORM) (° F.) T_(LIQ) (° F.) ΔT (° F.) NIST 714 T_(FORM) (° F.) 2214 2212 2212 2203 2205 2183 2201 2203 T_(LIQ) (° F.) 2116 2107 2095 2109 2077 2084 2098 2091 ΔT (° F.) 98 105 117 94 128 99 103 112 Ex. 91 Ex. 92 Ex. 93 Ex. 94 Ex. 95 Ex. 96 Ex. 97 Ex. 98 SiO₂ (wt %) 58.00 58.10 58.30 57.60 56.25 55.75 56.00 57.75 Al₂O₃ (wt %) 13.03 13.03 13.03 13.23 13.20 13.20 13.60 13.20 CaO (wt %) 23.84 23.74 23.54 23.84 23.75 23.25 24.25 24.25 MgO (wt %) 2.50 2.50 2.50 2.50 2.50 2.55 2.50 2.55 TiO₂ (wt %) 0.50 0.50 0.50 0.50 1.10 1.10 0.50 1.10 B₂O₃ (wt %) 1.00 1.00 1.00 1.20 2.00 3.00 2.00 Na₂O (wt %) 0.10 0.90 0.90 0.90 0.90 Li₂O (wt %) 0.90 0.90 0.90 0.80 ZnO (wt %) MnO(wt %) MnO₂ (wt %) Fe₂O₃ (wt %) 0.23 0.23 0.23 0.23 0.25 0.25 0.25 0.25 SiO₂/RO 2.20 2.21 2.24 2.19 2.14 2.16 2.09 2.15 NIST 717A T_(FORM) (° F.) T_(LIQ) (° F.) ΔT (° F.) NIST 714 T_(FORM) (° F.) 2178 2181 2183 2185 2235 2199 2215 2250 T_(LIQ) (° F.) 2079 2075 2084 2071 2100 2060 2077 2131 ΔT (° F.) 99 106 99 114 135 139 138 119 **average of two samples

Table 9 includes several glass fiber melt compositions made in a commercial glass melting operation. The amount of each constituent in the table is the weight percent in the actual melt. The weight percent for the Li₂O was determined using wet chemical analysis techniques, the weight percent for the B₂O₃ was determined using Neutron Transmission analysis techniques, and the weight percent for the remaining constituents was determined using X-ray fluorescence analysis (also referred to as “XRF analysis”), all of which are well know to those skilled in the art.

TABLE 9 Ex. 99 Ex. 100 Ex. 101 Ex. 102 SiO₂ (wt %) 57.97 56.83 58.57 58.46 Al₂O₃ (wt %) 12.28 13.28 12.44 12.32 CaO (wt %) 24.15 23.71 23.85 23.70 MgO (wt %) 2.6 2.45 2.42 2.48 TiO₂ (wt %) 1.16 0.55 0.51 0.50 B₂O₃ (wt %) 2.10 1.37 1.2 Na₂O (wt %) 0.89 0.87 Li₂O (wt %) 0.84 0.88 K₂O (wt %) 0.06 0.06 0.07 0.07 Fe₂O₃ (wt %) 0.28 0.28 0.27 0.275 SiO₂/RO 2.17 2.17 2.23 2.23 NIST 714 T_(FORM) (° F.) 2253 2224 2183 2185 T_(LIQ) (° F.) 2140 2061 2082 2080 ΔT (° F.) 113 164 101 105

Based on the above, in one nonlimiting embodiment of the present invention, the glass fiber compositions have a base composition of SiO₂, CaO, Al₂O₃ and Fe₂O₃, and optionally Na₂O, as discussed above, and a MgO content ranging from 1.7 to 2.9 wt %, preferably from 1.8 to 2.9 wt %, and more preferably 1.8 to 2.7. In another nonlimiting embodiment, the glass fiber compositions have a MgO content ranging from 1.7 to 2.7 wt %, and preferably from 1.9 to 2.65 wt %.

In one nonlimiting embodiment of the invention, for glass compositions that do not include any liquidus temperature reducing additives other than MgO or only trace amounts of these additive, i.e. less than 0.05 wt, the MgO range is 2.2 to 2.9, preferably from 2.4 to 2.8 wt %, and more 2.45 to 2.65 wt %. In another embodiment of glass compositions with little or no liquidus temperature reducing additives other than MgO, the MgO range is from 2.2 to 2.7, and preferably from 2.3 to 2.6 wt %.

In still another nonlimiting embodiment of the invention, in glass compositions that include a total amount of at least 0.05 wt % of liquidus temperature lowering additives, the MgO content ranges from 1.7 to 2.65 wt %, and preferably between 1.8 and 2.6 wt %, and more preferably 1.9 to 2.55 wt %. In another nonlimiting embodiment of glass compositions that include liquidus temperature lowering additives, the MgO content ranges from 1.7 to 2.5 wt %, and preferably between 1.8 and 2.3 wt %. In one nonlimiting embodiment of the present invention, the liquidus temperature lowering additives in the glass fiber compositions include, but are not limited to, Li₂O, ZnO, MnO, MnO₂ and/or B₂O₃ in the amounts discussed earlier.

It should be appreciated that although other commercially available glasses reduce environmental hazards due to boron and fluorine emissions by reducing or eliminating these materials from the batch, these glasses are processed at higher forming temperatures that conventional E-glass. As a result, they require additional energy for production. The present invention provides glass compositions that include little or no boron and/or fluorine and have a forming temperature generally lower than other low boron and/or fluorine glass compositions, and boron-free and fluorine-free glass compositions, and more specifically, have forming temperatures approaching that of E-glass. In one nonlimiting embodiment of the invention, the forming temperature of the glass compositions of the present invention should be no greater than 2280° F. (1249° C.), and preferably no greater than 2260° F. (1238° C.), and more preferably no greater than 2230° F. (1221° C.), based on the NIST 714 reference standard. In one particular nonlimiting embodiment of the invention, the forming temperature is no greater than 2200° F. (1204° C.), based on the NIST 714 reference standard.

In addition, in one nonlimiting embodiment of the present invention, the liquidus temperature of the glass compositions of the present invention should be no greater than 2155° F. (1179° C.), and preferably no greater than 2145° F. (1174° C.), and more preferably no greater than 2130° F. (1166° C.).

As discussed earlier, in the glass fiber forming industry, ΔT should be maintained in a range sufficient to prevent devitrification of the molten glass in the bushing area of a glass fiber forming operation and stagnant areas of the glass melting furnace. In the present invention, it ΔT should be at least 65° F. (36° C.), preferably at least 90° F. (50° C.), and more preferably at least 100° F. (56° C.). In addition, although not required, in order to maintain the overall heating and melting requirements of the glass fiber composition low, it is preferred that AT be no greater than 150° F. (83° C.) and more preferably no greater than 125° F. (69° C.). This will maintain a lower forming temperature for a given liquidus temperature and result in good energy efficiency. If required, the amounts of SiO₂ and CaO can be modified to change the forming temperature and provide a desired ΔT. More specifically, reducing the silica content while simultaneously maintaining or increasing the calcia content (thus reducing the SiO₂/RO ratio) will reduce the forming temperature and thus reduce ΔT. This type of modification would be of value if, for example, ΔT was much greater than 100° F. and could be reduced without adversely affecting the glass melting and forming operation. Conversely, increasing the silica content and while simultaneously maintaining or reducing the calcia content (thus increasing the SiO₂/RO ratio) will raise the forming temperature and thus increase ΔT. This type of modification would be of value if, for example, ΔT was too low and had to be increased to at least 100° F. Compositional adjustments of the silica and/or calcia (and the resulting SiO₂/RO ratio) in either direction are possible until the ΔT is obtained that is deemed to facilitate the pursuit of a safe industrial melt forming process.

As discussed above, the SiO₂/RO ratio can be manipulated to further assist in achieving the goal of lowering the overall processing temperature, and in particular lowering the forming temperature while providing a ΔT required to facilitate continuous fiber forming operation. Although not limiting in the present invention, the glass fiber compositions of the present invention have an SiO₂/RO ratio of no greater than 2.3, preferably no greater than 2.25, and more preferably no greater than 2.2.

The invention has been described with reference to specific embodiments, but it should be understood that variations and modifications that are known to those of skill in the art may be resorted to within the scope of the invention as defined by the claims. 

I claim:
 1. A glass fiber composition comprising: SiO₂ 52 to 59 percent by weight; Na₂O 0 to 2 percent by weight; CaO 16 to 25 percent by weight; Al₂O₃ 8 to 16 percent by weight Fe₂O₃ 0.05 to 0.80 percent by weight; K₂O 0 to 2 percent by weight; MgO 1.7 to 2.9 percent by weight; B₂O₃ 0.05 to 2 percent by weight; TiO₂ 0 to 2 percent by weight; and Li₂O 0.2 to 1 percent by weight;

wherein the glass composition has a weight ratio of SiO₂ to RO no greater than 2.3, wherein R is Ca and Mg.
 2. The glass fiber composition according to claim 1, wherein the glass composition has a forming temperature of no greater than 2200° F. based on an NIST 714 reference standard and a liquidus temperature of no greater than 2100° F.
 3. The glass fiber composition according to claim 1, wherein the glass composition has a forming temperature of no greater than 2190° F. based on an NIST 714 reference standard and a liquidus temperature of no greater than 2090° F.
 4. The glass fiber composition according to claim 1, wherein the MgO content is 2.2 to 2.9 percent by weight.
 5. The glass fiber composition according to claim 1, wherein the MgO content is 2.4 to 2.7 percent by weight.
 6. The glass fiber composition according to claim 1, wherein the glass composition has a B₂O₃ content of 0.5 to 1.5 percent by weight.
 7. The glass fiber composition according to claim 1, wherein the SiO₂ content is 52 to 59 percent by weight, the CaO content is 20 to 25 percent by weight, the Al₂O₃ content is 11 to 14 percent by weight, and the TiO₂ content is 0.5 to 2 percent by weight.
 8. The glass fiber composition according to claim 1, wherein the SiO₂ content is 57 to 59 percent by weight, the CaO content is 22 to 24 percent by weight, the Al₂O₃ content is 12 to 14 percent by weight, and the TiO₂ content is 0.5 to 1.5 percent by weight.
 9. A glass fiber composition consisting essentially of: SiO₂ 52 to 59 percent by weight; Na₂O 0 to 2 percent by weight; CaO 16 to 25 percent by weight; Al₂O₃ 8 to 16 percent by weight Fe₂O₃ 0.05 to 0.80 percent by weight; K₂O 0 to 2 percent by weight; MgO 1.7 to 2.9 percent by weight; B₂O₃ 0.05 to 2 percent by weight; TiO₂ 0 to 2 percent by weight; and Li₂O 0.2 to 1 percent by weight;

wherein the glass composition has a weight ratio of SiO₂ to RO no greater than 2.3, wherein R is Ca and Mg.
 10. The glass fiber composition according to claim 9, wherein the glass composition has a forming temperature of no greater than 2200° F. based on an NIST 714 reference standard and a liquidus temperature of no greater than 2100° F.
 11. The glass fiber composition according to claim 9, wherein the glass composition has a forming temperature of no greater than 2190° F. based on an NIST 714 reference standard and a liquidus temperature of no greater than 2090° F.
 12. The glass fiber composition according to claim 9, wherein the MgO content is 2.2 to 2.9 percent by weight.
 13. The glass fiber composition according to claim 9, wherein the MgO content is 2.4 to 2.7 percent by weight.
 14. The glass fiber composition according to claim 9, wherein the glass composition has a B₂O₃ content of 0.5 to 1.5 percent by weight.
 15. The glass fiber composition according to claim 9, wherein the SiO₂ content is 52 to 59 percent by weight, the CaO content is 20 to 25 percent by weight, the Al₂O₃ content is 11 to 14 percent by weight, and the TiO₂ content is 0.5 to 2 percent by weight.
 16. The glass fiber composition according to claim 9, wherein the SiO₂ content is 57 to 59 percent by weight, the CaO content is 22 to 24 percent by weight, the Al₂O₃ content is 12 to 14 percent by weight, and the TiO₂ content is 0.5 to 1.5 percent by weight.
 17. The glass fiber composition according to claim 9, wherein the composition has a ΔT of at least 65° F.
 18. A glass fiber composition comprising: SiO₂ 57 to 59 percent by weight; Na₂O 0 to 2 percent by weight; CaO 22 to 24 percent by weight; Al₂O₃ 12 to 14 percent by weight; Fe₂O₃ 0.05 to 0.80 percent by weight; K₂O 0 to 2 percent by weight; MgO 2.4 to 2.7 percent by weight; B₂O₃ 0.5 to 1.5 percent by weight; TiO₂ 0.5 to 1.5 percent by weight; and Li₂O 0.2 to 1 percent by weight;

wherein the glass composition has a weight ratio of SiO₂ to RO no greater than 2.3, wherein R is Ca and Mg.
 19. The glass fiber composition according to claim 18, wherein the glass composition has a forming temperature of no greater than 2200° F. based on an NIST 714 reference standard and a liquidus temperature of no greater than 2100° F.
 20. The glass fiber composition according to claim 18, wherein the glass composition has a forming temperature of no greater than 2190° F. based on an NIST 714 reference standard and a liquidus temperature of no greater than 2090° F.
 21. The glass fiber composition according to claim 19, wherein the composition has a ΔT of at least 65° F.
 22. The glass fiber composition according to claim 19, wherein the composition has a ΔT of at least 90° F. 